Abstract: The pacing system disclosed herein involves both an implantable, battery-powered heart stimulating unit and an external, patient-operable overdriver unit. Responsive to the application of the external unit, the implanted unit switches from an inhibit mode to a synchronous mode in which it is responsive to and tracks signals generated by the external unit thereby to apply externally selectable stimulation sequences for the treatment of tachycardia-type arrhythmias.

Abstract: A fully implantable programmable cardiac pacer includes two main pacing channels driven by a crystal oscillator circuit. For each channel, amplitude and pulse width are programmed in paired combinations corresponding to monotonically increasing charge density. Selectively combinable constant current sources are shared by each channel. A low battery indicator system samples battery voltage relative to two threshold levels. In magnet rate, if the main battery voltage is above the first threshold, the fixed pacer output will be 70 beats per minute. If the battery voltage is between the first and second threshold levels, the fixed pacer output will be 62.5 beats per minute. An emergency RC oscillator continuously produces an output at 52.5 beats per minute and one millisecond pulse width.

Abstract: A cardiac pacer employing the connector system disclosed herein is usable with either a unipolar lead or a bipolar lead provided with a plug at the proximal end having an extending pin portion to which a distal stimulating electrode is electrically connected. In the case of a bipolar electrode, an annular ring is provided on the plug to which the reference or indifferent electrode is connected. Respective clamping means are provided for establishing electrical connections to the pin and the annular ring, if present. A bridging means is provided for utilizing the pacer case as a reference potential when a unipolar lead is being used.

Abstract: The cardiac pacer disclosed herein responds to a premature heartbeat by first digitally measuring the time interval between a pair of successive sensed heartbeats and establishing an escape interval for stimulation which is shorter than the measured heartbeat interval. Pacing at this shorter escape interval enables the pacer to capture and control the heartbeat rate. By repeatedly incrementing the digital value representing the escape value on successive stimulated heartbeats, the heart is then caused to slow down until a preselected desired rate is established. Preferably, the sensing and timing between heartbeats continues during the slowdown process so that, if, at any time, a natural heartbeat occurs earlier than the stimulation pulse at the then extant escape interval, the escape interval is reset to a shorter time so that capture will be re-established.